Field of the Invention
Aspects of the present invention relate to a mold for manufacturing a dome-type cover for a surveillance camera that is manufactured by injection molding, and a method for manufacturing a dome-type cover.
Description of the Related Art
In recent years, network cameras for surveillance have become popular. A wide variety of cameras are installed everywhere, for example, in the street, public facilities, and individual houses. Some of such cameras are housed in dome-type covers. FIG. 8 is a schematic view of a camera having a dome-type cover. To depict the camera in the dome-type cover, part of the dome-type cover is removed. In the dome-type cover 4, a lens barrel 9 can be three-dimensionally freely turned by rotating it in the swiveling direction 2 and the vertical direction 1, and any photographing direction can be selected to perform surveillance.
The dome-type cover functions to protect the camera from deterioration due to weather and vandalism. The dome-type cover is also an exterior component and is also a part of the optical system of the camera. FIG. 3 shows an overall view of the dome-type cover alone. The hemispherical optical effective region 5 is a light-transmitting surface, and requires a shape accuracy as high as that required for lenses. The open end of the hemispherical surface is connected to a substantially cylindrical portion 6, and the end of the substantially cylindrical portion 6 has a flange portion 7. The substantially cylindrical portion 6 is a shape for expanding the volume of an inner housing portion housing the camera. The flange portion 7 is a shape for joining the dome-type cover to a cover lens barrel 8.
To accommodate mass production, dome-type covers are generally manufactured by plastic injection molding. Cup-type containers having a similar shape are generally molded in such a manner that a pin gate for a hot runner is disposed at the center (zenith) of a surface forming a cup, and the flow length from the center (zenith) to the open end circumference of the container, which is the flow end, is uniform.
In the case of a dome-type cover, the center (zenith) of the dome is a light-transmitting surface. Therefore, if a gate mark is left, it deforms the optical surface, and gets in the way of camera photographing. For this reason, the same manufacturing method as that used for manufacturing containers cannot be used for manufacturing a dome-type cover. As disclosed in Japanese Patent Laid-Open No. 2000-244782, a side gate is generally provided at one end of the flange portion.
In Japanese Patent Laid-Open No. 2000-244782, a stationary mold and a movable mold are depicted such that they are each formed by one mold member. That is, a cavity, a gate, and a runner are all processed in one mold member. However, since it is difficult to place a large mold member on a processing machine, the cavity part is generally processed separately, as a separate member (a convex surface mold, a concave surface mold).
FIG. 9 shows an example enlarged view of the surroundings of a cavity of a conventional injection mold for a dome-type cover. Reference numeral 23 denotes a stationary side attachment plate, reference numeral 24 denotes a stationary side die set, reference numeral 25 denotes a convex surface mold, reference numeral 26 denotes a sprue bush, reference numeral 28 denotes a movable side die set, reference numeral 29 denotes a concave surface mold, reference numeral 32 denotes a center pin, reference numeral 30 denotes a sprue, reference numeral 27 denotes a runner, reference numeral 33 denotes a gate, and reference numeral 31 denotes a cavity.
In recent years, the network camera performance have improved, and an improvement in magnification and an improvement in resolution are being desired. When the magnification of a camera is improved, the size of the lens barrel is increased. Therefore, it is necessary to accordingly increase the size of a dome-type cover for covering this. In order to reduce a decline in optical properties due to the interposition of plastic to improve the resolution, a reduction in wall thickness is required.
To injection-mold a large and thin dome-type cover, it is necessary to set the injection molding conditions to a high injection speed and high pressure because the flow length is long and the channel resistance is large.
When injection molding is performed using a mold such as that shown in FIG. 9, during the charging step, high-injection-speed and high-pressure resin flowing through the gate 33 presses the side surface 36 of the convex surface mold 25, and deforms the side surface 36. Because the optical surface of the convex surface mold 25 is processed by rotary cutting, so it is manufactured separately from the stationary side die set 24. Therefore, a fitting gap 37 exists between the convex surface mold 25 and the stationary side die set 24. For this reason, the above-described pressing force expands the gap 37.
As a result, resin flows into the gap 37, and a flash 39 is formed on the bottom surface 38 of the flange portion as shown in FIG. 10, which is a sectional view of the dome-type cover before removing a runner and gate.
The bottom surface 38 of the flange portion touches the camera main body. Therefore, when the flash 39 is formed, the attachment attitude of the dome-type cover is not stable. For this reason, the flash needs to be removed in post-processing, and the cost increases.
There is a case of a mold structure in which, to stabilize demolding, the convex surface mold 25 is slid out before demolding. In that case, flashes remain and accumulate on the sliding surface and interfere with mold operation, and productivity is lowered.